In a wireless network such as a third generation partnership project (3GPP) GPRS wireless network that operates according to a global system for mobile communications (GSM) standard ciphering of packet service (PS) data is performed in a logical link control (LLC) layer. Ciphering parameters that are needed for the ciphering to operate are negotiated between wireless communication devices and a network by a GPRS mobility management (GMM) entity. A GMM entity is a functional block that has an interface to a lower LLC layer in the communication protocol stack.
Due to various disturbing effects on radio signals carrying the enciphered data along a radio path of an uplink and/or downlink between a wireless communication device and the wireless network, the ciphering may get unsynchronized. That is, data that has been enciphered at the wireless communication device cannot be deciphered at a receiving network node, and vice versa. When this occurs, neither the wireless communication device, nor the network node is able to receive anything successfully. This typically leads to a data connection between the entities being aborted and the wireless communication device enters an idle state. If this situation occurs during a GMM routing area update procedure, then it is a severe drawback since the wireless communication device is in such a situation not able to register itself in a packet domain. For example, this will lead to a permanent packet service (PS) registration failure as the wireless communication device will never be able to receive routing area update accept messages in a downlink direction and, as a consequence, the wireless communication device will keep on retransmitting routing area update requests. This issue can be seen in case of buggy networks and in an IRAT scenario where a wireless communication device moves from, e.g., a third or fourth generation radio network to a GPRS network. Sometimes in such scenarios a wireless communication device is not able to get a correct ciphering key and it is thereby not able to decipher received enciphered downlink data and hence it will be unable to register successfully in the GPRS network.
In United States patent application publication US2004/0053623 problems with unsynchronized ciphering parameters are discussed. Ciphering is re-synchronized by way of specific LLC signaling between a mobile station and a serving GPRS support node.